Lysosomal storage diseases are a group of over thirty individual lethal inborn errors of metabolism (Glew et al., 1985, Laboratory Investigation 53:250-269). The diseases are typically caused by either deficient synthesis, or synthesis in a functionally-defective form, of any of various intracellular enzymes important in the metabolic or catabolic functions of the cell. Within the lysosomes of certain cells of people suffering from lysosomal storage diseases, are abnormally accumulated substances such as lipids and/or polysaccharides. The accumulation of these substances intracellularly can cause cell and organ dysfunction resulting in a range of clinical manifestations and may ultimately result in premature death.
Deficient enzyme activity, whether due to a defect in the synthesis of the enzyme or synthesis in a functionally-defective form, may be compensated for by the presence in sufficient quantities of the active enzyme. Enzyme replacement therapy for the purpose of metabolically correcting lysosomal storage disease has been attempted in both human clinical trials and animal model studies (Tager et al., pp.343-359 in Enzyme Therapy in Genetic Diseases, Alan R. Liss, New York, 1980; Grabowski et al., pp.167-208 in Enzymes as Drugs, John Wiley & Sons, New York, 1981; Brady, R. O., pp. 181-193 in Genetics of Neurological and Psychiatric Disorders, Raven Press, New York, 1983).
A major problem encountered in both the human clinical trials and the animal model studies was the virtual exclusive clearance of the administered enzyme by the liver. Current modes of enzyme replacement therapy, involving the injection of an active form of the enzyme into the body of an individual suffering from a lysosomal storage disease, have several problems in addition to rapid clearance from the body. Repeated injections of enzyme derived from a heterologous species may lead to the subsequent development of a hypersensitivity reaction by the individual. Development of such an immune response by the individual may not only undesirably enhance the clearance of the enzyme, but also may result in a clinically manifested, life-threatening reaction. Another problem is the potential for bio-inactivation of the administered enzyme by proteolytic enzymes found circulating in the bloodstream. To compensate for rapid clearance from the body, or for bio-inactivation, and because the administered enzyme is not specifically targeted to the cells containing deficient enzyme activity, the active enzyme has been administered in quantities much greater than the body needs. This in turn may undesirably increase the chances of developing a hypersensitivity reaction.
One strategy for improved delivery of active enzymes has involved exploitation of receptor-mediated uptake systems of cells (Poznansky, M. J., 1983, Pharmac. Ther. 21, 53-76). Receptor-mediated uptake (adsorptive endocytosis) refers to the cellular uptake of macromolecules for which there are binding sites accessable on the plasma membrane or outer surface of a cell. Recent attempts of enzyme replacement therapy for Gaucher's disease, a lysosomal storage disease, utilizing receptor-mediated uptake include modifying the carbohydrate moiety of the enzyme glucocerebrosidase by deglycosylation to produce an enzyme preparation with potential for specificity in receptor binding (Barton et al., 1990, Proc. Natl. Acad. Sci. USA 87:1913-1916). While administration of the altered enzyme appeared to result in some clinical improvement, there is a need for a composition which would facilitated more efficient uptake of the active enzyme than accomplished by free enzyme alone, in efforts to improve enzyme replacement thereapy.
Lectins, proteins having specific carbohydrate-binding activity, have been suggested as transport vehicles potentially useful for the targeted delivery of therapeutic agents (Shier, W. T. pp. 43-70, in Drug Carriers in Biology and Medicine, Academic Press, London, 1979. U.S. Pat. No. 4,749,570 discloses the approach of targeting delivery of enzymes by the use of a targeting agent-enzyme-albumin conjugate. The targeting agents disclosed are hormones, lectins, and cell-specific antibodies. The purpose of the albumin is to mask antigenicity of the conjugate. In U.S. Pat. No. 4,749,570, the conjugates were demonstrated to bind to their target cells, and in one instance to be internalized. It was not disclosed if all targeting agents used in U.S. Pat. No. 4,749,570 facilitated the uptake of the conjugate. In addition, where internalization was disclosed, it was not apparent that active enzyme reached and acted upon any accumulated substrate. Internalization of a complex such as a conjugate is just one step in the process of cellular enzyme replacement thereapy. Other crucial steps include avoiding interacellular digestion before enzyme action; reaching the appropriate cellular compartment(s) deficient in enzyme activity; and enzyme activity by the internalized complex on the appropriate endogenous substrate(s). Therefore a need exists for a composition that may facilitate the uptake of active enzyme by a cell deficient in enzyme activity, where the active enzyme reaches and acts on accumulated substrate, wherein the composition may not require a masking agent.
Another approach to treatment of genetic diseases is gene therapy. In this approach, genes or nucleic acids are introduced in attempts to replace poor or mutant gene expression. Standard gene therapy involves either injection of genes encoding a therapeutic protein; or removing cells from an affected individual, engineering the cells with new genetic material, and replacing the cells in the body. Problems encountered when injecting genes as a therapeutic treatment include degradation of the nucleic acids before they reach the target cells, and inefficient uptake of nucleic acid constructs by target cells. Problems encountered with genetically engineering cells removed from an individual are difficulties in getting nucleic acids into the cells without destruction or contamination of the cells and difficulties of targeting the genetically engineered cells to the regions of the body which may be sites for therapy.
Thus, a composition containing genes encoding a normal or functional enzyme which will serve to replace poor or mutant gene expression and which may overcome the problems of standard gene therapy is desirable for gene therapy of lysosomal storage diseases.
Additionally, there may be certain lysosomal storage diseases in which a mutant form of the lysosomal enzyme is produced which lacks enzymatic function but which may block the activity of newly introduced functional enzyme. Therapy of such diseases may require inactivation of the mutant gene in addition to introduction of functional enzyme. One approach utilizes antisense technology to inactivate the mutant gene. Since only the sense strand of DNA codes for the mutant enzyme, short oligonucleotides of the complementary strand, the antisense strand, may be used to bind to m-RNA or DNA to block their function in the cell thereby modulating mutant enzyme production. Thus, a composition which can deliver and facilitate uptake of oligonucleotides may be useful in antisense therapy of lysosomal storage diseases.